Implants for creating connections to tissue parts, in particular to skeletal parts, as well as device and method for implantation thereof

ABSTRACT

A method for locating a material having thermoplastic properties in pores of bone tissue includes providing a pin having the material having thermoplastic properties and a core, wherein the material having thermoplastic properties is arranged on the circumferential surface of the core constituting an outer region of the pin. An opening is provided in the bone tissue, and the pin is positioned at least partly in the opening. The outer region of the pin is then impinged with mechanical vibration energy for a time sufficient for liquefying at least part of the material having thermoplastic properties, and, in a liquefied state, pressing it into the pores of the bone tissue surrounding the opening. The vibration energy is stopped for a time sufficient for re-solidification of the liquefied material, and then the core is removed.

BACKGROUND OF THE INVENTION

The invention relates to implants for humans or animals. The implants atleast partly create positive-fit connections to human or animal tissueparts, particularly skeletal parts, wherein the implants help connecttissue parts together, or help connect tissue parts to means supportingor replacing tissue parts, or to other therapeutic auxiliary devices.The invention further relates to devices and methods for implantingimplants into humans or animals.

Known implants for creating connections to skeletal parts (bones)include screws, pins, agraffes etc., which are used for connecting bonesto bones, or bones to artificial, carrying, stabilizing, or supportingparts, or to parts replacing skeletal parts (stabilization or fixationplates, sutures, wires, artificial joint elements, artificial teeth,etc.). Such connection elements for implantation consist for example ofmetal or plastic, including resorbable plastic. After healing, theconnection elements are removed by a further operation or they are leftin the body where they are possibly gradually decomposed and replaced byvital tissue.

For stabilizing a bone fracture, a fixation plate with suitable holes isfixed in the region of the fracture using screws as mentioned above.Plate and screws may consist of metal (e.g. stainless steel ortitanium). The screws are self-cutting and are rotated into threadlessopenings in the bone, or they are screwed into pre-drilled threadedopenings. Pins and agraffes are knocked into previously created openingsfor similar purposes. Connections created in the foregoing manner areusually based on frictional engagement, possibly on positive fit.

In all cases, large forces (torsional forces and impact forces) are tobe applied on implantation, and possibly also on removal. This oftenmeans that the implants need to have a higher mechanical stability forimplantation and removal, than for the load which they are to bear whenimplanted. In particular, for implants of resorbable plastic, which havea significantly lower mechanical strength than metal, this increasedrequirement for mechanical stability requires the implants to haverelatively large cross sections, and thus, for implantation, undesirablylarge openings need to be created in the vital tissue.

Implantation of the named connection elements may also generateconsiderable quantities of heat and therewith impair the surroundingtissue, in particular due to the friction generated when producing africtional engagement. This applies in particular to the cutting ofthreads, the screwing-in of self-cutting screws and the knocking-in ofimplants without prior drilling.

It is known also to use curable, plastic materials (e.g. particularcements on a hydraulic or polymer base) for creating connections of thementioned type. Such materials are pressed from the outside betweenimplant and vital tissue, or into tissue defects in a highly viscouscondition, and are cured in situ. Positive-fit connections can becreated using such material, if the openings into which the material ispressed comprise suitable undercuts.

It is the object of the invention to provide implants for creatingpositive-fit connections to tissue parts (in particular to bone parts,cartilage parts, tendon parts, ligament parts, but also to parts ofother tissues), wherein the implants are able to be implanted in asimple, quick manner, with small forces, and wherein the implants areable to provide very stable connections immediately after implantation(primary stability). Furthermore, it is desired that the implants createfewer problems with regard to the generation of heat and formation ofstress concentrations than is the case with at least some of the knownimplants, and that the volume of foreign material to be implanted isreduced. It is a further object of the invention to provide a device anda method for implanting the implants.

SUMMARY OF THE INVENTION

The objects are achieved by the implants, the device and the method ofthe present invention.

The invention exploits the per se known fact (e.g. from the publicationWO-98/42988), that in particular, thermoplastic polymer materials can beliquefied in a targeted manner by way of mechanical oscillation and, inthis condition, can be pressed into cavities (e.g. pores of wood) by wayof hydrostatic pressure, thereby creating positive fit connections aftersolidification.

According to the invention, the implants serving for creatingpositive-fit connections to tissue parts consist at least partly of amaterial that can be liquefied at a relatively low temperature (<250°C.) by way of mechanical oscillation energy (in particular ultrasound),i.e. by internal and/or external friction, such that the material can bepressed into pores or other openings of the tissue part by the effect ofexternal pressure to form positive-fit connections when re-solidified.

Polymers which plasticize at relatively low temperatures are suitable asthe material to be liquefied by mechanical energy in the implantsaccording to the invention, in particular thermoplasts which are alreadyknown to be medically applicable. Such thermoplasts, being nonresorbable are for example: polyethylene (PE), polymethyl metacrylate(PMME), polycarbonate (PC), polyamide, polyester, polyacrylates andcorresponding copolymers. Such thermoplasts being resorbable are forexample polymers based on lactic acid and/or glycolic acid (PLA, PLLA,PGA, PLGA etc.), as well as polyhydroxyalkanoates (PHA),polycaprolactones (PCL), polysaccharides, polydioxanones (PD),polyanhydrides and corresponding copolymers. Per se known hydraulic orpolymeric cements having thixotropic properties are likewise suitable:for example, calcium phosphate cements, calcium sulphate cements andmethacrylate cements. Such cements may also contain thixotropicallyprepared, native tissue or transplanted materials. Due to theirthixotropic properties, such cements can be brought from a highlyviscous condition to a fluid condition by applying mechanical energy (inparticular ultrasound) and without an increase in temperature.

For implantation, the implant according to the invention is brought intocontact with the tissue part (on the surface or in an opening, which asthe case may be, has been created specially for the implant), and isthen impinged with ultrasound energy and at the same time is pressedagainst the tissue part. By a suitable design of the implant and by asuitable metering of the energy, it is ensured that only a requiredminimum amount of the liquefiable material is liquefied in a locallytargeted manner. As soon as sufficient material is liquefied and pressedinto place, the supply of energy is stopped so that the liquefiedmaterial solidifies in its new shape, with the pressure on the implantbeing advantageously maintained.

For implantation, the mentioned materials are thus not liquefied byexternal heat, but by mechanical energy (oscillation energy, vibrationenergy), i.e. as a result of internal and/or external friction. As aresult, the thermal burden to the surrounding tissue remains low. A veryhigh shear effect is achieved between different material phases by wayof the mechanical energy. This contributes to the uniform liquefactionand achievement of low viscosity and still low burdening of thesurrounding. The material liquefied in this manner is then pressed intopores or openings of the surrounding tissue by way of hydrostaticpressure, thereby permeating the surrounding tissue and enforcing it.

If so required, it may be advantageous to admix additional substances tothe liquefiable material for additional functions. For example,substances may be admixed that mechanically reinforce the liquefiablematerial, that let the liquefiable material swell up in a secondaryreaction or form pores therein, or that are to be released into thevital surroundings for promoting healing or regeneration, or that are toassume other functions. Such healing-promoting andregeneration-promoting substances may, for example be growth factors,antibiotics or inflammation-inhibitors. Such substances can be broughtto a desired location or may be distributed in a tissue region in atargeted manner by the flow of the liquefied material, and in the caseof a resorbable material, may be set free in a delayed manner.

Using connection implants according to the invention, pointwise orlarger-surface connections can be realized. The load distribution on theconnection can be influenced and controlled in a targeted manner. Forexample, with implants according to the invention, it is possible tofasten a fixation or stabilization plate on a bone surface either over alarge surface (see e.g. FIG. 15 or 16) or pointwise and depth-effective(see FIGS. 2 to 4). More superficial connections may be achieved withplates or other support or fixation devices having integratedliquefaction zones or complete liquefaction layers, which for connectionto a bone are positioned on the bone and are subsequently excited withmechanical energy (e.g. ultrasound vibration), at least locally. Theliquefiable regions are advantageously provided with energy directors,or are in contact with energy directors. Energy directors that encouragelocal liquefaction by concentrating the oscillation energy areprojecting elements, e.g. pyramids, conical, hemispherical or rib-likeelements.

Depth-effective anchorages are achieved by pin-like or dowel-likeimplants that have a cross section (or cross-sectional geometry) that isconstant or changes over their length, and that completely or partlyconsist of the liquefiable material. They are positioned on the surfaceof the tissue or in the tissue and are then excited. These implants areadvantageously designed such that liquefaction starts at predefinedlocations (tip or specific stem regions). Controlled liquefaction mayalso be achieved by energy directors (projecting elements shaped in adefined manner). Depth-effective anchoring is achieved by bringing theimplant into the tissue to be connected. The hydrostatic conditions canbe such that the liquefied material is pressed into the adjacent tissueunder a large pressure.

The device for implanting the implant according to the invention, i.e.,the device for liquefying the liquefiable material in contact with thetissue part, and for pressing it into the tissue, may additionallyoperate to control the temperature in surrounding tissue and material,such that unreasonable quantities of heat and high temperatures andtissue damage caused thereby can be prevented. The implantation processis controlled by actively controlling the device with regard to suppliedand removed energy (heat distribution and heat management) and, whereappropriate, by suitably arranged sensors and heat conducting elements.Such implantation is controlled by metering the supplied energy and bydissipating excess energy.

The energy used for material liquefaction is preferably produced bypiezoelectric or magneto restrictive excitation. An oscillation unit(e.g. piezoelement plus sonotrode) is actively connected to the implant(pressed against it) and is oscillated by a generator, which transmitswaves in the frequency region of about 2 to 200 kHz, preferablyultrasound (e.g. 20 or 40 kHz). The implant is coupled to the bone ortissue to be connected in a manner such that the sound energy isabsorbed internally or on the surface by the liquefiable material, whichis thereby liquefied at least locally. The liquefaction process isachieved by a large shear effect. Internal friction and, thus, internalliquefaction can be enhanced by a second component having a differentdensity and being locally embedded in the material to be liquefied (e.g.as globules). The same effect is exploited when using a thixotropic,particulate cement as an implant or implant part.

The connections produced by the method according to the invention aremainly positive fit connections, wherein the positive fit means may bevery small on both sides (surface irregularities, surface roughness, ortissue pores) or larger (larger cavities in the tissue or between tissueparts or mechanically created openings or cavities in the tissue). Theconnection implants are mechanically excited by way of ultrasound in amanner such that they are liquefied in a controlled manner in particularin the contact region with the tissue part or in their interior.Liquefaction usually takes place on a tissue surface or in a suitableopening in the tissue, which opening is formed by penetrating theconnection implant through the tissue surface after implantation, or bypenetrating the connection implant before implantation.

The incorporation of the liquefiable material into the tissue in adepth-effective manner can in a very simplified and schematic way becompared with the effect of a piston in a hydraulic cylinder. The notyet liquefied material of the connection implant is seated in a tissueopening and essentially fills and seals it. Since the liquefied materialcannot escape from the opening, a hydrostatic pressure is created onaccount of the load acting from the outside (pressure on the implant).Due to the pressure and the oscillation the liquefied material ispressed into existing and/or newly formed cavities of the surroundingmaterial to be connected (vital tissue). The penetration depth depends,inter alia, on the nature of these surroundings, on the operatingparameters and on the liquefiable material (in particular itsviscosity). The quantity of material pressed into the tissue can bedetermined through the liquefiable or liquefied volume of the connectionimplant. If a lot of liquefied material is required, or the size andnumber of the cavities present in the tissue is not known, it ispossible to use implants or implant components that can be suppliedquasi infinitely.

Stress peaks produced by the displaced and compressed material, whichmay lead to failure, e.g. bursting of the tissue, are avoided bytargeted application of ultrasound and mechanical or hydrostaticpressure, the two being coordinated to one another, as well as by asuitable design of the implants and the liquefiable materials arrangedthereon. Cavities and gaps in the tissue are filled by the liquefiedmaterial, in the case of sufficiently porous tissue, even withoutpre-drilling. At the same time, the tissue in contact with theliquefiable material is compressed in a controlled manner such that theresulting retention of the connection implant is strong even in heavilyporous tissue (e.g. osteoporotic bone tissue). Through the describedeffects, the implant according to the invention can resist largemechanical drawing forces or loads. In a later phase of the healingprocess, loading is reduced in a controlled manner or is taken over byregenerated tissue (secondary stabilization) if the implant is made atleast partly of resorbable material.

The invention is suitable for example for anchoring a tooth prosthesisin a jaw. The tooth prosthesis preferably comprises a standardized basepart designed as an implant according to the invention and beingconnectable to various crown parts. The base part consists completely orpartly of a material being liquefiable by mechanical energy. Whenpositioned in an opening in the jaw bone, this material is liquefied byexcitation with mechanical energy and is pressed into pores of the bonetissue. As a result, the implant adapts itself to the opening and to thetissue pores, is stabilized immediately after implantation (primarystabilization) and is well-anchored, not only in the tooth root opening,but also in the adjacent bone tissue, thereby forming a suitable basepart for fastening the crown part. If the liquefiable material isresorbable, the aforementioned primary stability is later, at leastpartly, replaced by a secondary stabilization due to regenerated bonetissue.

A further field of application of the invention is in the field ofartificial joint elements. An artificial joint socket as well as a jointball or its stem may be connected to the vital bone tissue or anchoredtherein by way of implants according to the invention. In addition tothe gentle transmission of the loads on implantation, the materialstaking part are selected such that increases in stiffness are largelyavoided, which contributes positively to the life duration of theimplant.

The device used for the implantation of the implant according to theinvention comprises a generator for producing electrical oscillation tobe transmitted to an oscillation unit via transmission means, e.g. acable. The oscillation unit comprises an oscillation element (driveunit) and a resonator, the two being actively connected to one another.The drive unit (e.g. piezoelement) excites the resonator intooscillation. The oscillation of the resonator is transmitted to theimplant directly or via a transmission means. Due to the oscillation,the implant is liquefied at least locally by inner liquefaction or bycontact with a non-oscillating environment (tissue part or anotherimplant part). During excitation, the implant may be held using asuitable holder and/or may be guided by way of a guide element. Forminimally-invasive surgery, it is particularly suitable to fasten theimplant directly on the oscillation unit. Holding and/or guide means maybe provided, not only for temporarily holding or fixing the implant, butalso for temperature management (in particular heat dissipation).

Due to the way in which the material of the implant is liquefied in atargeted and local manner, no large quantities of heat are produced.Additionally, the temperature of the tissue regions adjacent to theimplant may be actively controlled by way of temperature management, forexample by way of heat conducting elements, which act to dissipate heatin a targeted manner, or by way of cooling fluids (e.g. sterile ringersolution) which act in a temperature-controlling manner.

The method for implantation of the implant according to the invention onthe human or animal skeleton is carried out as follows: the implant isbought into contact with the skeleton part, then mechanical oscillationsare produced and transmitted to the liquefiable material of the implantwhilst the implant is pressed against the skeleton part. Mechanicalenergy is supplied until the liquefiable material is sufficientlyliquefied, and in the region of contact, penetrates into the bonetissue, or at least the surface irregularities of the skeleton part. Themechanical oscillation is then stopped for re-solidification of theliquefied material, during which it is advantageous to maintain thehydrostatic pressure. The re-solidified material anchors the implant inthe skeleton part with a positive fit.

The connection implants according to the invention have the shape ofpins, dowels and/or plates or films. These serve the connection oftissue parts amongst one another, or of tissue parts to artificialelements.

For implantations of the above-described manner, it is advantageous touse a kit or a set comprising at least one type of implant according tothe invention, advantageously a selection of variously dimensionedimplants suitable for the field of application, as well as a device forcarrying out the implantation. Advantageously, the kit also comprisesmeans for the sterile use of the device (sterile coverings for thedevice) and, as the case may be, exchange pieces of components (inparticular resonator, distal resonator part or transmission part) beingable to be sterilized. By way of different shapes, the resonator partsare adapted to various implants and/or applications. Furthermore, thekit advantageously comprises instructions for implantation, details onimplantation parameters and further auxiliary means for preparing thetissue part (e.g. drills matched to the implants), positioninginstruments, control instruments and/or implant guides adapted toimplants and/or resonators.

The kit or set is preferably kept complete by subsequent provision ofimplants. The selection is made according to the demands and may changewith time. The subsequent provision of implants (replacement andaddition kit) comprises replacements for used implants, as well as theprovision of new implant types and again includes suitable means fortissue preparation, positioning instruments, control instruments,adapted resonators or resonator parts, implant guides and, inparticular, corresponding implantation instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail by way of the subsequentFigures, wherein:

FIG. 1 shows an exemplary embodiment of the device for implantingimplants according to the invention, and its use;

FIG. 2 shows a fixation plate fastened on a bone by implants accordingto the invention;

FIGS. 3 and 4 show examples of implants according to the invention, tobe used e.g. in the application according to FIG. 2, and connectionsbetween bone and plate created therewith;

FIGS. 5 a to 5 d show exemplary cross sections of pin-like implantsaccording to the invention, wherein the implants comprise axiallyextending energy directors;

FIGS. 6 to 8 show longitudinal sections through two exemplary, pin-likeimplants according to the invention, wherein the implants compriseimplant parts of a non-liquifiable material;

FIGS. 9 to 13 show exemplary embodiments of cooperating holding means onpin-like or dowel-like implants and resonators;

FIG. 14 shows applications of implants according to the invention on ahuman scull or jawbone;

FIGS. 15 to 17 show implants applicable e.g. in the scull region andexemplary connections between two scull parts created therewith;

FIG. 18 shows an exemplary resonator arrangement for applications asshown in FIGS. 16 and 17;

FIG. 19 shows a further application of implants according to theinvention in the region of the human vertebral column;

FIG. 20 shows a further application of implants according to theinvention for fixing a tooth replacement;

FIGS. 21 and 22 show in section two exemplary implants according to theinvention suitable for the application as shown in FIG. 20;

FIG. 23 shows a fixation device fixed to a forearm bone by implantsaccording to the invention;

FIG. 24 shows an example of a connection implant suitable for theapplication as shown in FIG. 23;

FIG. 25 shows in section the fixation device according to FIG. 23 beingfastened on a bone by implants according to FIG. 24;

FIG. 26 shows a further example of a connection implant suitable for theapplication as shown in FIG. 23;

FIG. 27 shows a trochanter plate for fixing a broken neck of a joint,wherein the plate is fixed with the help of an implant according to theinvention;

FIG. 28 shows a stem for an artificial joint ball, wherein the stem isfastened to a tubular bone with an implant according to the invention;

FIG. 29 shows a joint ligament being fastened to bones by implantsaccording to the invention;

FIG. 30 shows a section through a tissue cavity, for example caused by atumor, wherein the cavity is to be filled with an implant according tothe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Schematically, and in a very simplified manner, FIG. 1 shows anexemplary embodiment of an implantation device 1 applicable forimplanting implants according to the invention.

The device 1 comprises a generator 2 and an oscillation unit 3 connectedtogether via a cable 4. The oscillation unit 3, which is partlyaccommodated in a housing 5, is designed as a hand apparatus to be usedlike a hand drill, for example. The oscillation unit 3 comprises anoscillation element integrated in the housing 5 (not shown in detail)and actively connected to a resonator (sonotrode) 6. At least a distalresonator part projects out of the housing 5. The generator 2 suppliesthe oscillation element with energy. Excited by the oscillation element,the resonator oscillates at a predefined frequency or, as the case maybe, with a predefined frequency pattern. Frequencies of 2 to 200 Hz andresonator amplitudes of 1 to 100 μm in the direction (z-direction)indicated by the double arrow are particularly suitable. The frequenciesmay be set depending on the application, the materials to be liquefiedand the shape of resonator and implant. It is also conceivable tosuperimpose additional mechanical oscillations, such as with a lowerfrequency and larger amplitude on the vibrations in the ultrasoundregion. In many cases, it is sufficient to design the device for asingle oscillation frequency, for example for 20 or 40 kHz and for aresonator amplitude of approximately 20 or 30 μm in the z-direction(direction in which an implant 7 is pressed by the resonator 6 against atissue part). In order to control the power (supplied energy per unit oftime), the excitation may be pulsed, wherein pulse distances and/orpulse lengths are set.

Advantageously, and in a per se known manner, the oscillation frequencyand the resonator shape are matched to one another such that theresonator oscillates in a standing wave and such that its distal end,which is pressed against the implant, has a maximum amplitude in thez-direction. It is further advantageous to give pin-like implants alength that is matched to a predefined excitation frequency andpredefined implant material.

The distal end of the resonator 6 may be designed for holding an implant7, as is shown in FIG. 1. This simplifies positioning of the implant ona tissue part or in an opening of a tissue part, such as the bone of aleg 10. For positioning and implantation without an opening, it may alsobe advantageous to provide an implant guide that is supported on thehousing 5 or on the tissue part. It is also possible to design theresonator with a planar end face like a hammer and to simply press itagainst an implant held in a tissue opening or held by way of a suitableseparate mounting or guide means. The distal end face of such aresonator must not stick to the implant during implantation. This isachieved by a suitable, non-adhering end-face of the resonator or by animplant part adjoining the resonator part that consists of a nonliquefiable material.

For applications in a sterile operation region, the device may be usedin a sterile covering. Advantageously, the sterile covering comprises anopening for the distal part of the resonator, and the resonator or adistal resonator part can be removed for exchange and sterilization.

Other exemplary embodiments of the implantation device 1 according tothe invention can be designed as hand-held apparatus comprising allcomponents (including energy supply) or as completely stationaryapparatus.

FIG. 2 shows a fixation or stabilization plate 21 being fastened byimplants 7 according to the invention on a bone part in the region of abone fracture or laceration, in order to stabilize the fracture orlaceration. The bone part 20 in this case comprises a relatively thin,but relatively compact, outer cortical layer 22 disposed abovecancellous bone tissue 23 which is porous. Other than shown in FIG. 2,the transition of the cortical bone to the cancellous bone in naturaltissue is a gradual transition in which the tissue becomes more and moreporous. The implants 7 extend through openings in the plate 2, throughthe cortical bone substance 22 and into the cancellous bone 23 and theyare anchored at least in the cancellous bone 23.

FIGS. 3 and 4 in section and in an enlarged scale, show two examples ofimplants according to the invention that may be used for the applicationshown in FIG. 2. FIG. 3 shows an implant after implantation. FIG. 4shows another implant that is positioned in an opening 24 of plate 21and cortical bone substance 22 and is ready for impingement withoscillation energy.

For implantation, at least the cortical substance layer is to be opened,for example by drilling. A suitable bore may also continue into thecancellous bone 23 as a pocket hole. Since the cortical substance of thebone has no suitable pores for pressing in the liquefied material, suchopenings or surface irregularities may be created by cutting a thread 25or by roughening the inner walls of the bore. The liquefied material isthen pressed into such openings and re-solidified to form a positive-fitconnection. The liquefied material of the implant is pressed into thepores of the cancellous bone 23, and, in this manner, the implant 7 isanchored in a depth-effective manner. It shows that hydrostaticallypressing a liquid material into the tissue pores is significantlygentler on the tissue than mechanically introducing a solid material.For this reason, it is possible to create stable connections to tissuenot having much mechanical strength, e.g., to osteoporotic bone tissue.

In order to connect the implant 7 to the plate 21, the implant may havea head that is like a mechanical screw, such as is shown in FIG. 2. Asshown in FIG. 3, the opening in the metallic plate 21 may also comprisean inner thread that is like the thread created in the corticalsubstance 22 of the bone. The liquefied material penetrates andsolidifies in these threads, thereby forming a positive fit. In thiscase, an implant head is not needed. The implant 7 is aligned flush tothe plate 21 by driving a suitably dimensioned implant to the desiredposition, thereby avoiding undesirable trimming of a projecting implantpart.

For a plate 2 consisting of a thermoplastic plastic, the connectionbetween plate and implant (securement against loosening) may beaccomplished as shown in FIG. 4, wherein a material-fit connection(welding or adhering) is formed at the same time the implant is anchoredin the tissue. On driving in the implant, this material-fit connectionbegins to form at the connection location 26. In this case as well, theimplant 7 is advantageously driven so far in that, in the end, it isflush with the outer side of the plate 21.

Since the implant 7 does not need to be rotated into the tissue, it doesnot need to include means for coupling in a relatively large torsionalforce, as is as required for known screws. Dimensioning of the implantscan therefore be determined purely by their function in the implantedcondition. As such, the implants are more streamline and the openingsthat need to be created in the tissue are smaller than is the case withconventional screws of the same material. Since the positive-fit isformed by liquefaction and resolidification of the material, itcomprises less stress and notches, which further increases its strengthand makes it less prone to material fatigue.

Implants according to the invention to be anchored in the tissue part ina depth-effective manner, as shown in FIGS. 2 to 4, are advantageouslypin-like or dowel-like and comprise the liquefiable material for exampleat their distal end, as well as on further surface regions at which ananchoring is desirable (e.g. in a thread in plate 21 and corticalsubstance 2 of the bone). In fact, as shown in FIGS. 2 to 4, theimplants may completely consist of the liquefiable material, wherein thedistal end and the surface regions at which the material is to beliquefied in particular are advantageously provided with energydirectors, or energy directors are provided at surfaces coming intocontact with these regions. Such energy directors may be distal implantends that are pointed or taper to one or more essentially point-like orlinear tip regions. Further surface regions to be liquefied may includehumps, tips or ribs whose height and widths are to be adapted to theanchoring being created. The energy directors project at least 10 μmbeyond the surface. They may also be significantly larger and may bedesigned as axially-running ribs rendering the pin cross section humpedor cornered, as is shown in an exemplary way by FIGS. 5 a to 5 d.Pin-like implants have such cross sections over their entire length, oronly over a part of their length.

For pin-like implants to be anchored in the region of their cylindricalsurface only, or in addition to anchoring in the region of the distalend, tissue openings (e.g. bores) are provided such that introduction ofthe implant causes (at least locally) a friction fit between tissue andimplant or energy directors respectively, i.e. the tissue openings areslightly narrower than the cross section of the implants.

For further functions, the liquefiable material may contain foreignphases or further substances. In particular, the material ismechanically strengthened by admixture of fibers or whiskers (e.g.calcium phosphate ceramics or glasses). The liquefiable material mayfurther comprise in situ swelling or dissolvable, i.e. pore-formingconstituents (e.g. polyester, polysaccharides, hydrogels, sodiumphosphate) and substances to be released in situ, e.g. growth factors,antibiotics, inflammation reducers or buffers (e.g. sodium phosphate) tocombat the negative effects of an acidic breakdown. Admixtures forfurthering visibility in x-ray pictures and similar functions areconceivable also.

It has been shown that when anchoring implants in cancellous bone(wherein the implants have a construction according to FIGS. 2 to 4, arecomposed of polymers such as PC or PLLA and have a diameter of 3 to 4mm) forces in the region of 0.5 to 5 N per mm² implant cross section areadvantageously used for the pressing-in. Forces in the named rangeresult in a driving-in speed greater than 5 mm/s.

FIGS. 6 to 8 show three further, exemplary pin-like implants 7, which,in addition to regions of liquefiable material, comprise a core 11(FIGS. 6 and 7) or a sleeve 13 (FIG. 8) composed of a non-liquefiablematerial, such as metal, ceramic or glass, or a composite material.

The implants according to FIGS. 6 and 7 comprise at their distal end acap 12 of the liquefiable material, which is more or less pointed (FIG.6) or comprises a plurality of pointed or linear end regions (FIG. 7).The cylindrical surface of the core 11 is completely surrounded byliquefiable material (FIG. 6) or only in regions, wherein these regionsextend axially, or annular (FIG. 7) or may be regularly or irregularlydistributed over the core surface. These regions advantageously compriseenergy directors as described above for implants consisting entirely ofliquefiable material. The liquefiable material is to be thicker orthinner, depending on the desired penetration depth, but should not bethinner than approx. 10 μm.

Step-like reductions in cross section as shown in FIG. 6 are suitable asenergy directors. Implants with such steps are advantageously implantedin correspondingly stepped or narrowing tissue openings.

The impingement of a pin-like or dowel-like implant with anon-liquefiable core 11 may either concern the complete proximal end ofthe implant or only the annular outer region consisting of theliquefiable material.

The implant according to FIG. 8 comprises the liquefiable material inthe inside of a non-liquefiable sleeve 13. The sleeve 13 is providedwith openings arranged in places where anchoring is desired. Such anembodiment of the implant according to the invention is suitable inparticular for the application of highly viscous, thixotropic materialsas liquefiable material since such a material cannot withstand themechanical loading caused by the resonator pressing on the implant. Theopenings in the sleeve are to be dimensioned in a manner such that thehighly viscous material can only get through when liquefied. Sleeves 13of porous sintered material are particularly suitable. An implant with asleeve 13 is to be positioned in a tissue opening and the resonator isapplied only on the liquefiable material, i.e. has a cross sectionadapted to the inner cross section of the sleeve.

At the proximal end of a pin-like or dowel-like implant there may beprovided a head-like thickening, an artificial part replacing or fixinga further tissue part, a therapeutic auxiliary device, fastening meansfor such a device, or a fixation means for a suture or cerclage wire.The proximal end may also be equipped as a holding means cooperatingwith a corresponding holding means on the resonator (see FIGS. 9 to 11).

A metallic core 11, for example in a pin-like or dowel-like implant,usually serves as a mechanical reinforcement of the implant and issuitably dimensioned for this application. The core may, however, alsobe significantly thinner and easily removable from the implant. In thiscase, it provides visibility in an x-ray picture duringminimally-invasive implantation, and may serve as a guide wire. The coreis removed directly after implantation.

An implant comprising a metallic core and being anchored in the tissueaccording to the invention and comprising a liquefiable material that isresorbable has a good primary stability immediately after implantation.On resorption of the anchoring material, the anchoring loosens or ismade dynamic, such that more and more load has to be carried by thetissue itself. This encourages the regeneration process and prevents theatrophy process in many cases. After decomposition of the liquefiablematerial, the core can be removed easily if its surface is designed suchthat the vital tissue does not grow together with it. If its surface,however, is designed in a manner such that tissue intergrowth ispromoted (bioactive surface), this intergrowth constitutes an ideal,secondary stability for an implant or implant core remaining in thetissue (see also FIG. 28).

Implant cores as shown in FIGS. 6 and 7 may not only consist of metal(e.g. steels, titanium or cobalt-chrome alloys), but according to theirapplication, may also consist of polymers (e.g. polyetheraryl ketone,polyfluoro- and/or polychloroethylene, polyetherimides,polyethersulphones, polyvinylchlorides, polyurethanes, polysulphones,polyester) or of ceramic or glass-like materials (e.g. aluminium oxide,zirconium oxide, silicates, calcium phosphate ceramics or glass) or ofcomposite materials (e.g. carbon fibre reinforced high-temperaturethermoplasts).

FIGS. 9 to 13 show various exemplary applications for holding a pin-likeor dowel-like implant according to the invention in or at the distalpart of the resonator 6 (sonotrode) of the implantation device 1 (FIG.1). The holder may for example be a positive-fit holder as shown inFIGS. 9 and 10. The positive-fit for example is realized as asnap-closure (FIG. 9) of a resiliently designed proximal extension 14 ofan implant core 11 or implant 7 which is introduced into a correspondingopening 15 at the distal end of the resonator 6. The positive-fit mayalso be realized by a suitably secured pin 16 extending through theresonator 6 and the proximal extension 14 of an implant core 11 orimplant. Advantageously, the positive-fit is arranged at a distance d tothe distal end of the resonator such that it lies in a node point of theoscillations in z-direction, i.e. in a position in which the amplitudein z-direction is essentially zero.

FIG. 11 shows a screwed connection 17 between resonator 6 and implant 7,i.e. a non-positive fit or force-fit connection. If this connection isbiased in a manner such that the oscillations propagate uninterruptedfrom the resonator to the implant, the implant 7 becomes a part of theresonator 6 and is to be designed accordingly. This means that thedistal end of the resonator does not necessarily require maximalamplitude in the z-direction, but may as well lie on a node point.

FIGS. 12 and 13 show advantageous implant holders on the resonator 6 forimplants whose proximal end consists of the liquefiable material. Inboth cases, the proximal implant end is shaped by and bonded to thedistal end of the resonator 6 due to the ultrasound effect and suitableenergy directors arranged on the resonator. FIG. 12 shows a resonator 6with a distal surface which is formed as the impact surface of agranulating hammer. FIG. 13 shows a resonator 6 with a central energydirector. In both cases, the proximal end of the implant 7 is contactedby the energy directors of the resonator 6 and the resonator is set intooscillation. The liquefiable material in the region of the energydirectors of the resonator is liquefied first and bonds to theresonator, wherein it assumes the shape of its distal surface and formsa head 18 in the case which is shown in FIG. 12.

Holding of the implant on the resonator as shown in FIGS. 9 to 13 isadvantageously established before positioning the implant on or in thetissue part, and it is released after implantation, in the cases ofFIGS. 12 and 13, by way of a force with which the resonator is bent awayor rotated off the implant 7.

As an example of further fields of application for implants according tothe invention, FIG. 14 shows the fixation of a cover plate 30 of bone orof a man-made material into an opening of the calvaria 29 and thefixation for example of an artificial fixation plate 31 on a broken orfractured jawbone 32. Similar applications are conceivable inreconstruction surgery in the facial region. The connections that are tobe created between the cover plate 30 and the surrounding bone tissueare advantageously limited to selected locations of the gap 33 betweenthe plate and the native bone. The fixation plate 31 is likewiseconnected to the jawbone at selected plate locations 31′. Theconnections at the selected locations are realized in successiveimplantation steps using the implantation device 1.

In section and in an enlarged scale, FIGS. 15 to 17 show connectionsthat may be created with implants 7 according to the invention and that,for example, are suitable for the applications shown in FIG. 14.

FIG. 15 shows an implant 7 according to the invention that may be usedto provide at least a local connection between the scull 29 and thecover plate 30, which is to be fixed in an opening of the scull that maycontain porous material (e.g. likewise scull bone). The implant 7 ispositioned (above) and then implanted by way of ultrasound energy(double arrow) in order to connect the scull 29 and the cover plate 30across the gap 33 (below).

The gap 33 is advantageously formed obliquely in a manner such thatexternal pressure forces on the gap region are accommodated by thecalvaria 29. On the outer side, the gap 33 is extended for positioningthe implant 7. The implant, which for example, is spherical orsausage-like and consists of a thermoplastic or thixotropic material, ispositioned in the extended outer gap region and is impinged withoscillation energy. As a result, the implant material is liquefied, andon the one side, is pressed into the pores of the calvaria 29, and onthe other side, is pressed into corresponding pores of a cover plate 30consisting of, for example, bone, or into correspondingly arrangedartificially created openings (e.g. dot-dashed groove) in an artificialplate. A positive-fit anchoring is thereby created on both sides suchconnecting calvaria 29 and cover plate 30.

FIG. 16 shows a fixation foil 35 which may also have the form of atextile web and which may, for example, be applied for local fixation ofthe cover plate 30 in the opening of the scull 29. The foil 35 is, forexample, tape-like and is advantageously flexible. It consistscompletely of a liquefiable thermoplast or is, for example, reinforcedwith a fiber mat, or with a similar structure. It is applied over thegap 33 and is excited on both sides (double arrows) with the help of animplantation device (FIG. 1) in a manner such that it adheres to thesurface of the calvaria 29 and the surface of the cover plate 30(larger-surfaced, less depth-effective connection which may be limitedto a multitude or a pattern of individual fixation points). As the casemay be, the surface regions, at which the implant is to be connected tothe material lying therebelow, may be suitably pre-treated (e.g.roughened) or suitable surface structures (surface unevennesses,recesses, grooves etc.) are provided on the artificial plate 30. Inorder to conncet the film 35 to a bone surface, a pressure on the orderof 0.5 to 3 N per mm² of resonator end face is sufficient.

FIG. 17 shows a fixation plate 36 that is fastened with the help of afixation film 35 or corresponding textile web over the gap 33 and which,for accommodating accordingly larger forces, consists e.g. of metal.Therefore, in addition to being used in a skull application, thefixation plate 36 may also be used on the jaw as shown in FIG. 13 or inthe application according to FIG. 2. The fixation plate 36 consists of amaterial that is not liquefiable in the context of the invention. On asurface directed towards the tissue to be fixed, the fixation plate 36has a surface structure suitable for a positive fit. The film 35 ispositioned between the plate 36 and the tissue or material to be fixedand through the plate 36 is impinged at least locally with oscillationenergy and is thus connected to the surface of the calvaria 29 and tothe cover plate 30. The positive-fit connection between film 35 andfixation plate 36 may be created during implantation, or the plate 36with the film 35 already connected to it may be used as a finishedimplant. In such a two-layer implant the connection between the layersmay also be of a material fit (adhesion or welding). The film 35 in sucha two-layer implant may also be reduced to a coating of the plate,wherein the coating advantageously does not have a constant thickness,but has energy directors consisting of a pattern of humps, points orribs that have a minimal height (coating thickness) of approx. 10 μm.

The fixation plate 31 shown in FIG. 14 comprises film regions 31′arranged for example in suitable recesses and having an outer surfaceprovided with energy directors. These film regions are connected to thejawbone regions lying thereunder.

It may be advantageous for the application shown in FIG. 16 to designthe resonator to be used in a manner such that the oscillationstransmitted to the implant are not aligned perpendicular (z-direction)to the connection plane to be created as indicated with double arrows,but parallel to this (x/y-direction). As the case may be, a transmissionelement 37 as shown in FIG. 18 is suitable. This transmission element 37is connected to the resonator 6 with a non-positive fit and specificallyat a location in which the wave in the z-direction has a node point(amplitude=0) and thus the wave in the x/y direction has a maximumamplitude. This oscillation in the x/y direction is transmitted to thefilm 35 by the transmission element 37.

Schematically and in a greatly simplified manner, FIG. 19 shows afurther application of implants according to the invention, namely asupport element for a human vertebral column region. The support element40 is elastic and supports the vertebral column region in a lasting orpossibly temporary manner. In the context of the invention, the supportelement 40 is fastened to vertebral bodies in that it consists of acorrespondingly liquefiable material and is fastened without deptheffectiveness (as shown in FIG. 16), in that it consists of anon-liquefiable material and is connected to the vertebral bodiesthrough a film and without depth effectiveness (as shown in FIG. 17) orwith predrilling and depth effectiveness (as shown in FIGS. 2 to 4). Thepin-like implants 7 shown in FIG. 19 have, for example, a headprojecting beyond the support element and are made according to FIG. 13.For a lasting support, connecting implants and support element are madeof a non-resorbable material. For a temporary support, connectingimplants and support elements are made of a resorbable material.

FIG. 20 shows the application of a dowel-like implant 7 according to theinvention forming a basis for an artificial tooth 40 in a jawbone 32.The implant 7 consists, at least partly, of a thermoplastic orthixotropic material. On its end face, it comprises means for holdingthe artificial tooth 40, a bridge or prosthesis. The implant ispositioned in the corresponding opening with or without the artificialtooth and is pressed in further under ultrasound vibration. Since at thesame time at least a part of the implant liquefies, it not only fillsgaps between implant and bone in a largely interstice-free manner, butis also pressed into the pores of the jawbone so that a depth-effectiveconnection arises as is for example shown in section in FIG. 21.

FIG. 22 shows in section a further exemplary embodiment of an implantaccording to the invention. This implant is particularly suitable forthe application shown in FIG. 20. The liquefiable material is notarranged on the outer surface of the implant, but within a sleeve 13which is permeable to the liquefiable material when liquefied, as hasalready been described in connection with FIG. 8. The longitudinallysectioned implant is shown to the left of the middle line in a statebefore application of ultrasound and to the right of the middle line ina state after the application of ultrasound. The sleeve 13 consists, forexample, of a metallic or ceramic sintered material with an openporosity, and assumes the bearing function of the implant. In the showncase, it comprises an opening with an inner thread suitable forfastening a tooth, bridge or tooth prosthesis. The implant comprises afurther, annular opening 43 in which the liquefiable material ispositioned, for example a cylindrical piece 44 of the liquefiablematerial. For a targeted liquefaction, energy directors 45 are providedin the inside of the annular opening 43 in contact with the liquefiablematerial.

The implant according to FIG. 22 is, for example, positioned in anopening of a jawbone (41, FIG. 20) and then the liquefiable material isimpinged with mechanical energy using a resonator 6 with an annulardistal end. As a result, this material is liquefied and pressed throughthe porous sleeve material, into the surrounding bone tissue, wherebythe implant is anchored in this tissue.

For the application shown in FIGS. 19 to 20, it is particularlyadvantageous to select a resorbable material as the liquefiablematerial, whilst the bearing part consists of a material that is neitherliquefiable nor resorbable and that has a sufficient mechanical strengthfor the fastening of a tooth, bridge or prosthesis. At the same time, atleast the surface of the central part is bioactive (e.g. porous asdescribed for the sleeve 13), that is to say, equipped in a manner suchthat it promotes an intergrowth with bone tissue. Immediately afterimplantation, such an implant has a primary stability that is adequatefor fastening the tooth, bridge or prosthesis and for normal usethereof. Promoted by the bioactive surface of the central implant part,regenerated tissue then successively replaces the resorbable materialand grows together with the central implant part. The implant accordingto the invention thus offers an immediate primary stability without theapplication of cement and, after a resorption and regeneration phase apermanent secondary stability, which is equal to the stability of knownimplants. In comparison to known implantation methods, however, there isno transition phase in which, according to the state of the art, theopening 41 is closed and one waits for regeneration of bone tissuebefore the tooth, the bridge or the prosthesis is fastened directly inthe regenerated bone.

FIG. 23 shows an external fixation device 51 comprising supports 52 anda carrier 53 fastened on the supports 52, which device is for examplefastened on a tubular bone 50 of a human arm according to the invention.The supports 52 are designed as implants according to the invention. Themedial part of a tubular bone consists mainly of cortical bone substanceand comprises only very little tissue regions that are porous in thecontext of the invention. For this reason, the marrow space 54 in theinside of the tubular bone 50 is used for the liquefied material to bepressed into. This is shown in FIGS. 24 and 25 in more detail. Thesupports are provided for example with base plates 55 since the marrowcannot counteract the hydrostatic pressure with sufficient resistance.

In order to fasten the fixation device, openings (with a thread 25 asthe case may be) are drilled through the tubular bone 50 extending intothe marrow space, wherein the bore diameter corresponds to the diameterof the implant 7 or the base plate 55 respectively. The implant 7comprises a central support 52, a distal end fastened to the base plate55, and an annular or tubular region 57 of the liquefiable materialarranged around the support and essentially covering the base plate 55.The implant is introduced into the opening 56 and is held at apredefined depth with suitable means to be applied externally. Then theliquefiable material 57 around the support 52 is pressed against thebase plate 55 under the effect of ultrasound, so that it is pressedbetween the bone 50 and the base plate 55 into the marrow space 54 andthus forms a positive-fit connection holding the support 52 in theopening 56. This anchoring permits a unicortical fastening of thesupport 52, wherein the fastening is secure against tilting. Accordingto the state of the art, such fastening can be achieved only by abicortical fastening.

FIG. 26 shows a further embodiment of the implant 7 according to theinvention, wherein the is particularly suitable for the applicationshown in FIG. 23. The liquefiable material, which for example is athixotropic cement, is arranged in the inside of the support 52, andopenings 58 are provided above the base plate 55 and have a size suchthat the cement cannot exit in its highly viscous form, but exits in itsliquefied form by the effect of the resonator 6. The end of the support52 is designed as a sleeve in the sense of the sleeve according to FIG.8. The cement pressed through the openings 58 with the help of theresonator secures the support in the marrow cavity, and as the case maybe, in the adjacent bone tissue.

The implant according to the invention shown in FIG. 27 is a tensionscrew 60, which, for example, is used together with a trochanter plateto fix a broken femoral neck bone. The tension screw 60 (in the sense ofan implant sleeve 13, FIG. 8) is hollow and at least in its distal endcomprises openings through which a liquefied material can be pressed outin order to anchor this distal region better in osteoporotic bone tissuethan is possible alone with the thread of the tension screw. The threadof the screw thus serves in particular for pulling together the tissuein the region of the fracture, until the distal screw end is anchored inthe tissue by the liquefiable material.

FIG. 28 shows, in a very schematic sectional representation, a tubularbone 50 on which an artificial joint element 62 is fastened by way of animplant 7 according to the invention. The stem 63 of the joint element62 and liquefiable material 57 arranged around the stem represent theimplant according to the invention, which is pressed into the tubularbone 50 under the effect of ultrasound, wherein the material 57 isliquefied and is pressed into pores of the cancellous bone 23 and intounevennesses of the inner surface of the cortical substance 22 of thetubular bone. The stem 63 has a surface structure which is suitable fora positive fit connection to the liquefiable material 57, in the samemanner as shown for plate 36 in FIG. 17.

A particularly advantageous embodiment of the stem 63 consists, forexample, of titanium and has a porous surface that is thus bioactive andit is surrounded by resorbable liquefiable material. Such an implant hasa primary stability directly after implantation, which permits at leastpartial loading. The primary stability is later taken over by asecondary stability effected by the intergrowth of vital bone tissueinto the porous surface of the titanium stem 63. This means that theartificial joint element may be loaded essentially immediately afterimplantation, but without the use of cement. This early loading favorsregeneration of the vital tissue and prevents atrophy (osteoporosis).All the same, in a further phase, vital tissue intergrows with thetitanium stem.

FIG. 29 likewise very schematically shows a joint 70 in the region ofwhich a ligament 71 connects the bones 72 and 73. The ligament 71 isnaturally intergrown with the bone, wherein this connection may tear onoverloading. Implants 7 according to the invention can be used for therepair, wherein implant embodiments according to FIGS. 2 to 4 may beused. For the repair, the cortical substance of the joint bone is openedand pin-like implants 7 are driven through the ligament 71 and securedexternally with a head (e.g. according to FIG. 13). Embodiments withless depth effectiveness according to FIGS. 16 and 17 are alsoconceivable.

Concluding, FIG. 30 shows that the connection to be created with theimplant 7 according to the invention need not necessarily serve theconnection of two elements (two tissue parts or a tissue part and anartificial part). It is also conceivable to use an implant according tothe invention for filling a tissue opening 80 being caused by a tumourfor example. For such an application, an implant 7 of a highly viscousand thixotropic material 81 is used. With the aid of a guide 82 beingpositioned around the opening, this material is introduced into theopening 18 such that it projects beyond the opening. The resonator 6used for this application has a cross section corresponding to the innercross section of the guide 82 and presses the material 81 into theopening 80 like a piston. The opening 80 is thereby not only filledessentially without interstices, but the material 81 becoming liquidunder the effect of ultrasound is also pressed into the tissue poresopening into the opening 80, and thereby forms a positive fit connectionafter solidification, which is shown below in FIG. 30. This positive-fitconnection securely holds the implant 7 in its opening 80 even withoutthe opening comprising undercuts, and without providing other retainingmeans (e.g. periosteum sutured above the implant).

Suitably, finely processed bone material of the patient may be admixedto the liquefiable material.

If in a case as shown in FIG. 30 a thermoplastic material is usedinstead of the thixotropic cement, the opening 80 may also be speciallymanufactured for accommodating a fixation element for a wire 84 orsuture, as shown dot-dashed in FIG. 30 (only below). A therapeuticauxiliary device, such as a stimulator, may be fixed in the same manner.

Example 1

Pins of PLLA and polycarbonate manufactured by injection molding andhaving a round cross section of diameters between 3.5 and 4.25 mm, alength of 26 to 40 mm (ideal length at 20 kHz: 35 mm), obtusely tapered,distal ends and four grooves axially extending over 10 mm from thedistal end were anchored with an excitation frequency of 20 kHz incancellous bone (femur head) of freshly slaughtered cattle. Forimplantation, the thin cortical substance layer lying over thecancellous bone was opened, but the cancellous bone was not pre-drilled.On implantation, the implants were pressed against the tissue withpressures of 60 to 130 N and excited with the excitation frequency(sonotrode amplitude approx. 20 to 25 μm). The advance was limited to 10mm which was achieved in less than 2 s. The implants were then heldwithout excitation for 5 seconds.

The resulting anchorage depths were in the order of 15 mm and theanchorage on tearing out proved to be stronger than the implantsthemselves (maximum tear-out forces over 500 N). Sensors being placed at1 mm from the pre-bore in the cortical bone substance (1.5 mm below thebone surface) recorded temperatures of max. 44° C. (approx. 22° aboveroom temperature) approx. 10 s after implantation. The temperature risewas reduced to half its value in approximately 30 seconds.

No molecular weight reduction was found in the implanted PLLA materialwhen compared with the material before implantation.

What is claimed is:
 1. A method for locating a material havingthermoplastic properties in pores of bone tissue in a human or animalbody, the method comprising the steps of: providing a pin comprising thematerial having thermoplastic properties and a core, wherein the corecomprises a distal end and a proximal end and a circumferential surfacetherebetween, wherein the material having thermoplastic properties isarranged on the circumferential surface of the core constituting anouter region of the pin, and wherein the material having thermoplasticproperties is liquefiable with the aid of mechanical vibration energy,providing an opening in the bone tissue, the opening being adapted tothe pin, positioning the pin at least partly in the opening, impingingthe outer region of the positioned pin with the mechanical vibrationenergy for a time sufficient for liquefying at least part of thematerial having thermoplastic properties, and, in a liquefied state,pressing it into the pores of the bone tissue surrounding the opening,stopping the vibration energy for a time sufficient forre-solidification of the liquefied material, and, after the step ofstopping, removing the core.
 2. The method according to claim 1, whereinthe outer region of the pin surrounds the core completely and thereforeis annular and wherein, in the step of impinging and in the step ofstopping, a vibration tool with a corresponding annular distal face isused.
 3. The method according to claim 1, wherein the bone tissuesurrounding the opening is fortified by the thermoplastic material. 4.The method according to claim 1, wherein the core consists of a furthermaterial which is not liquefiable by the mechanical vibration energyused in the step of impinging.
 5. The method according to claim 1,wherein the material having thermoplastic properties is additionallyarranged on the distal end of the core.
 6. The method according to claim1, and further comprising a step of anchoring an artificial support orfixation element in the resolidified material having thermoplasticproperties.
 7. The method according to claim 1 and further comprising astep of connecting another tissue part or a means for supporting orreplacing another tissue part to the resolidified material havingthermoplastic properties.
 8. The method according to claim 1, whereinthe material having thermoplastic properties is a biodegradablematerial.
 9. The method according to claim 8, wherein the biodegradablematerial comprises a polymer based on at least one of lactic acid andglycolic acid.
 10. A method for fastening a first and a second objectrelative to bone tissue in a human or animal body with the aid of amaterial having thermoplastic properties and being liquefiable byapplication of mechanical vibration energy, the method comprising thesteps of: providing the first and second objects, wherein the firstobject comprises a first surface portion of a first material havingthermoplastic properties and at least one of the first and secondobjects comprises a second surface region of a second material havingthermoplastic properties, positioning the first and the second objectsrelative to each other and relative to the bone tissue such that thefirst surface region faces the bone tissue and the second surface regionfaces a third surface region of the other one of the first and secondobjects, impinging the first or the second object with the mechanicalvibration energy for a time sufficient for liquefying at least parts ofthe first and second surface portions while bringing the first surfaceportion into contact with the bone tissue and the second surface portioninto contact with the third surface portion, stopping the mechanicalvibration energy for a time sufficient for re-solidification of theliquefied material while keeping the first surface portion in contactwith the bone tissue and the second surface portion in contact with thethird surface portion, wherein, in the step of impinging and in the stepof stopping, connections are established between the first surfaceportion and the bone tissue and between the second surface portion andthe third surface portion.
 11. The method according to claim 10, whereinthe second material having thermoplastic properties is comprised by thefirst object and wherein the first and second materials havingthermoplastic properties are the same material.
 12. The method accordingto claim 10, wherein the third surface portion comprises a thirdmaterial having thermoplastic properties being weldable to the secondmaterial having thermoplastic properties and wherein the connectionestablished between the second and third surface portions is a weldedconnection.
 13. The method according to claim 12, wherein the second andthe third materials having thermoplastic properties are the samematerial.
 14. The method according to claim 10, wherein the thirdsurface portion comprises a surface structure into which the liquefiedsecond material having thermoplastic properties is pressed during thestep of impinging, and wherein the connection established between thesecond and the third surface portions is a positive fit connection. 15.The method according to claim 14, wherein said surface structurecomprises openings, cavities, pores, grooves or a thread.
 16. The methodaccording to claim 10, wherein the first object is a pin, wherein thesecond object comprises a through opening adapted to the pin, wherein,during the step of positioning, the pin is positioned to extend throughthe through opening, and wherein, for the step of impinging, the pin isimpinged with the mechanical vibration energy.
 17. The method accordingto claim 16, wherein the first and second surface portions are arrangedon the pin, wherein the first and second materials having thermoplasticproperties are the same, and wherein the pin consists completely of thissame material.
 18. The method according to claim 17, wherein the throughopening comprises a thread which constitutes the third surface portion.19. The method according to claim 16, wherein, before the step ofpositioning, a bore is provided in the bone tissue, wherein during thestep of positioning, the pin is positioned through the through openingand at least partly into the bore.
 20. The method according to claim 10,wherein, during the step of positioning, the first object is positionedbetween the bone tissue and the second object, and wherein for the stepof impinging, the second object is impinged with the mechanicalvibration energy.
 21. The method according to claim 20, wherein thesecond object is a plate.
 22. The method according to claim 20, whereinthe second material having thermoplastic properties is arranged on thefirst object, and wherein the first and the second materials havingthermoplastic properties are the same material, and wherein the firstobject consists completely of said same material.
 23. The methodaccording to claim 20, wherein the first object is a film or a textileweb.
 24. The method according to claim 10, wherein at least one of thefirst and second material having thermoplastic properties is abiodegradable material.
 25. The method according to claim 24, whereinthe first and second object consist completely of the biodegradablematerial.
 26. The method according to claim 24, wherein thebiodegradable material comprises a polymer based on at least one oflactic acid and glycolic acid.